Differential signal transmission device

ABSTRACT

A differential signal transmission device transmits N differential signal pairs from a differential signal generator to a number of receiving terminals. The N differential signal pairs include N positive signals and N negative signals. The N positive signals are clustered at a first positive clustering point. The first positive clustering point is connected to a second positive clustering point via a first matching resistor. The second positive clustering point is grounded via a first grounding resistor, and outputs a number of positive signals to the number of receiving terminals respectively. The N negative signals are clustered at a first negative clustering point. The first negative clustering point is connected to a second negative clustering point via a second matching resistor. The second negative signal clustering point is grounded via a second grounding resistor, and outputs a number of negative signals to the number of receiving terminals respectively.

BACKGROUND

1. Technical Field

The present disclosure relates to differential signal transmissiondevices, and particularly to a differential clock signal transmissiondevice.

2. Description of Related Art

Clock signals are significant for an electronic device to synchronouslyactivate components in the electronic device. A number of differentialclock signal pairs from a differential clock signal generator should beequal to a number of receiving terminals when the differential clocksignal pairs are transmitted by a common signal transmission device. Forexample, the differential clock signal generator just can provide twodifferential clock signal pairs to two receiving terminals. If thenumber of the receiving terminals is more than two, voltages at thereceiving terminals may be too low and thereby unsatisfied to a requiredspecification. Additionally, each of the receiving terminals should begrounded via a resistor when the differential clock signal pairs aretransmitted by the common signal transmission device, which is costly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sketch diagram of an exemplary embodiment of a differentialsignal transmission device.

FIG. 2 shows an exemplary waveform graph of a differential signaltransmitted by the differential signal transmission device of FIG. 1.

DETAILED DESCRIPTION

Referring to FIG. 1, an exemplary embodiment of a differential signaltransmission device 100 includes a differential clock signal generator10, a first receiving terminal 20, a second receiving terminal 30, athird receiving terminal 40, a fourth receiving terminal 50, twomatching resistors R1 and R2, and two grounding resistors R3 and R4. Thedifferential signal transmission device 100 may be formed on a printedcircuit board.

The differential clock signal generator 10 provides two differentialclock signal pairs L1 and L2. The differential clock signal pair L1includes a positive signal L11 and a negative signal L12. Thedifferential clock signal pair L2 includes a positive signal L21 and anegative signal L22. The positive signals L11 and L21 are clustered at afirst positive clustering point P1. The negative signals L12 and L22 areclustered at a first negative clustering point P2.

The first positive clustering point P1 is connected to a second positiveclustering point P3 via the matching resistor R1. The second positiveclustering point P3 is grounded via the grounding resistor R3, andoutputs four positive signals L31, L41, L51, and L61. The first negativeclustering point P2 is connected to a second negative clustering pointP4 via the matching resistor R2. The second negative clustering point P4is grounded via the grounding resistor R4, and outputs four negativesignals L32, L42, L52, and L62.

The positive signal L31 and the negative signal L32 are combined to forma differential clock signal pair L3, and are provided to the firstreceiving terminal 20. The positive signal L41 and the negative L42 arecombined to form a differential clock signal pair L4, and are providedto the second receiving terminal 30. The positive signal L51 and thenegative L52 are combined to form a differential clock signal pair L5,and are provided to the third receiving terminal 40. The positive signalL61 and the negative L62 are combined to form a differential clocksignal pair L6, and are provided to the fourth receiving terminal 50.

Since the two differential clock signal pairs L1 and L2 from thedifferential clock signal generator 10 are provided for the receivingterminals 20-50 via the points P1-P4, which means that the differentialclock signal pairs L1 and L2 are clustered to be a signal, and then thesignal is divided into four differential clock signal pairs L3-L6.Therefore, clock phases of the four differential clock signal pairsL3-L6 are synchronous, which means that there is no phase differenceamong the differential clock signal pairs L3-L6.

The exemplary embodiment of the differential signal transmission device100 is also capable of providing the differential clock signal pairsL3-L6 with a required specification according to the determinedresistances of the grounding resistors R3 and R4. Further details abouthow to determine the resistances of the grounding resistors R3 and R4will be explained in further detail below.

Currents of the differential clock signal pairs L1 and L2 provided bythe differential clock signal generator 10 are both equal to a currentI. Resistances of the grounding resistors R3 and R4 are both equal to aresistance R. Therefore, a current passing through the groundingresistor R3 is 2I, a current passing through the grounding resistor R4is −2I, and a voltage Vin of each of the receiving terminals 20-50 isequal to a voltage difference between the second positive clusteringpoint P3 and the second negative clustering point P4. The voltage Vin isobtained according to Vin=(V+)−(V−)=2I*R3−(−2I)*R4=2I*(R3+R4)=4IR,wherein the V+ is a voltage at the second positive clustering point P3,and the V− is a voltage at the second negative clustering point P4.Therefore, for example, when the voltage Vin of each of the receivingterminals 20-50 is required to be about 700 millivolts (mV), and thecurrent I of each of the differential clock signal pairs L1, L2 is about7 milliamperes (mA), the resistance R of each of the grounding resistorsR3 and R4 can be determined according to R=Vin/4I=700 mV/4*7 mA=25 ohms.

Referring to FIG. 2, the differential signal transmission device 100 issimulated via a common simulation software, to determine whether thedifferential clock signal pairs L3-L6 satisfy a required specificationor not. In one exemplary embodiment, when a rise time and a fall time ofeach of the differential clock signal pairs L3-L6 are both between150˜700 picoseconds (ps), the differential clock signal pairs L3-L6 aredetermined to be acceptable. The rise time is defined as a period duringwhich a voltage of each of the differential clock signal pairs L3-L6rising from 245 mV to 455 mV. The fall time is defined as a periodduring which a voltage of each of the differential clock signal pairsL3-L6 falling from 455 mV to 245 mV. FIG. 2 illuminates that the risetime of each of the differential clock signal pairs L3-L6 is about278.429 ps, and the fall time of each of the differential clock signalpairs L3-L6 is about 467.525 ps. Therefore, the differential clocksignal pairs L3-L6 are acceptable.

In other exemplary embodiments, the differential clock signal generator10 can provide the differential clock signal pairs L1 and L2 both with acurrent I to two or three receiving terminals via the matching resistorsR1 and R2, and the grounding resistors R3 and R4. A voltage of each ofthe receiving terminals is still equal toVin=(V+)−(V−)=2I*R3-(−2I)*R4=2I*(R3+R4)=4IR; wherein R is the resistanceof each of the grounding resistors R3 and R4.

In another exemplary embodiment, the differential clock signal generator10 can provide three differential clock signal pairs all with a currentI to six receiving terminals via the matching resistors R1 and R2, andthe grounding resistors R3 and R4 both with a resistance Rx. If avoltage of each of the six receiving terminals should be still equal to4IR, which is the voltage Vin of each of the four receiving terminals20-50, the resistance Rx of each of the two grounding resistors R3 andR4 can be obtained according to 2Rx=4IR/31=4R/3=4*25/3=33.3 ohms,therefore Rx=16.7 ohms.

In summary, if a voltage at each of the receiving terminals is requiredto be V, and the differential clock signal generator 10 provides Ndifferential clock signal pairs all with a current I, a sum of theresistances of the grounding resistors R3 and R4 are equal to V/N*I. Thedifferential clock signal pairs can be acceptable via adjusting theresistances of the grounding resistors R3 and R4 when the number of thereceiving terminals is more than N. Since there is some voltage loss inthe signal transmission, the number of the positive signals from thesecond positive clustering point P3 and the number of the negativesignals from the second negative clustering point P4 both should bebetter to not greater than 2 N, therefore, the number of the receivingterminals is not greater than 2 N.

It is to be understood, however, that even though numerouscharacteristics and advantages of the present disclosure have been setforth in the foregoing description, together with details of thestructure and function of the disclosure, the disclosure is illustrativeonly, and changes may be made in details, especially in matters ofshape, size, and arrangement of parts within the principles of thedisclosure to the full extent indicated by the broad general meaning ofthe terms in which the appended claims are expressed.

1. A differential signal transmission device, comprising: a differentialsignal generator providing N differential signal pairs to a plurality ofreceiving terminals, wherein the N differential signal pairs comprises Npositive signals and N negative signals, the N positive signals areclustered at a first positive clustering point, and the N negativesignals are clustered at a first negative clustering point; wherein N isa natural number greater than 1; a first grounding resistor; a secondgrounding resistor; a first matching resistor connected between thefirst positive clustering point and a second positive clustering point;wherein the second positive clustering point is grounded via the firstgrounding resistor, and outputs a plurality of positive signals; and asecond matching resistor connected between the first negative clusteringpoint and a second negative clustering point; wherein the secondnegative clustering point is grounded via the second grounding resistor,and outputs a plurality of negative signals; wherein each of thereceiving terminals receives one of the plurality of positive signalsfrom the second positive clustering point, and one of the plurality ofnegative signals from the second negative clustering point.
 2. Thedifferential signal transmission device of claim 1, wherein theplurality of positive signals from the second positive clustering pointare corresponding to the plurality of negative signals from the secondnegative clustering point respectively, and the number of the pluralityof positive signals from the second positive clustering point and thenumber of the plurality of negative signals from the second negativeclustering point are both not greater than 2N.
 3. The differentialsignal transmission device of claim 1, wherein when a required voltageof each of the receiving terminals is V, and a current of each of the Ndifferential signal pairs from the differential signal generator is I, asum of resistances of the first and second grounding resistors isdetermined to be V/(N*I).